1. Field of the Invention
The present invention relates to the tuning of vibratory transducers, and, more particularly, to the tuning of speakers, including the speakers used in back-up alarms typically found on commercial vehicles and mobile equipment.
2. Description of the Prior Art
Vibratory transducers are devices that convert electric energy to kinetic energy. The resultant motion may by employed for a variety of purposes, including sound generation. This energy conversion is most efficient when the transducer is operating at its resonance frequency. Each vibratory transducer has its own particular resonance frequency to which it must be tuned for peak efficiency and maximum performance.
Vibratory transducers may be found, for example, in the speakers of back-up alarms which are coupled to commercial vehicles and other mobile equipment to warn passersby that the vehicle is operating in reverse. When activated, the back-up alarm generates a warning tone at a particular frequency. As described above, this frequency is preferably the resonance frequency of the transducer, thereby allowing the alarm""s speaker to produce the loudest possible volume for a given energy input.
Vibratory transducers may be tuned during manufacture by, for example, placing a potentiometer within the speaker circuit and adjusting the potentiometer until the resonance frequency is reached. After initial tuning, the potentiometer is sometimes sealed to prevent accidental or undesirable adjustments away from the resonance frequency. Unfortunately, a transducer""s resonance frequency will change with age and conditions of operation, including temperature and humidity. Thus, it is desirable to regularly re-tune a transducer. Even were the tuning mechanism not sealed, however, manual tuning is a time-consuming and inefficient process. More desirably, the transducer would re-tune itself. Various methods and apparatuses have been set forth which accomplish self-tuning. One common method involves comparing the phase of an input signal to the phase of the corresponding output signal, with zero phase difference indicating resonance. Other methods involve equating resonance with peak velocity or maximum displacement or vibration. These methods are generally suited to particular transducer applications or operating conditions, can require substantial additional hardware, and may yield results of questionable accuracy. Furthermore, many such methods require an intermediate input device, such as a microphone, for driving the speaker, which adds complexity, mass, and expense.
The method and apparatus of the present invention allow vibratory transducers, particularly speakers, including the speakers associated with back-up alarms, to frequently and regularly re-tune themselves to their resonance frequency. Broadly, the method and apparatus of the present invention operate by comparing the rising and falling edges of a test voltage waveform produced by the stimulated transducer.
More specifically, if the rising edge of a pulse of the voltage waveform is lower than the falling edge of the pulse, then the transducer is operating below its resonance frequency. If the rising edge of the voltage pulse is higher than the falling edge, then the transducer is operating above its resonance frequency. The closer the voltages are to being equivalent, the closer the transducer is to its resonance frequency. If the transducer is operating either above or below resonance, a simple electronic circuit in accordance with the present invention adjusts the operating frequency accordingly to more closely approach the resonance frequency.
By physically incorporating the simple electronic circuitry of the present invention into existing driver circuitry, the transducer is directly stimulated and tested without the need for microphones or other intermediate input devices commonly required by other methods and apparatuses. Thus, a vibratory transducer may be checked for resonance, and adjusted if needed, automatically, efficiently, without human intervention, and at frequent and regular intervals.
These and other important aspects of the present invention are more fully described in the section entitled DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT, below.